Aqueous film forming foam (AFFF) agents are known for the rapid extinguishment of Class B fires and enhancement of safety by providing flashback or burnback resistance. First described by Francen in U.S. Pat. No. 3,562,156, AFFF agents by definition must have a positive spreading coefficient on cyclohexane. Many U.S. patents describe the composition of AFFF agents which meet the positive spreading coefficient criteria, such as U.S. Pat. Nos. 4,420,434; 4,472,286; 4,999,119; 5,085,786 and 5,218,021; 5,616,273.
The prior art relating to AFFF agents has one common element; the requirement of various quantities and types of fluorochemical surfactants to obtain the positive spreading coefficient when combined with various hydrocarbon surfactants. U.S. Pat. No. 5,616,273 describes present AFFF and alcohol resistant aqueous film forming (AR-AFFF) agents used to generate aqueous film forming foams having fluorine contents ranging from 0.020 to 0.044 percent in premix form. The actual fluorine level has been dependant on the required performance specifications, with higher fluorine content providing faster extinguishing performance and greater burn back resistance. The lowest fluorine content product (0.020% F) would contain about 1.3% by weight fluorochemical surfactant solids in the 3% liquid concentrate since these products contain about 50% by weight fluorine.
The criterion necessary to attain spontaneous spreading of two immiscible liquids has been taught by Harkins et al, Journal Of American Chemistry, 44, 2665 (1922). The measure of the tendency for spontaneous spreading of an aqueous solution over the surface of non-polar solvents such as hydrocarbons is defined by the spreading coefficient (SC) and can be expressed as follows:SCa/b=γa−γb−γc, where  1)    SCa/b=Spreading Coefficient;    γa=Surface tension of the lower hydrocarbon phase;    γb=Surface tension of the upper aqueous phase; and    γc=Interfacial tension between the aqueous upper phase and the lower hydrocarbon phase.
If the SC is positive, in theory an aqueous solution should spread and film formation on top of the hydrocarbon surface should occur. The more positive the SC, the greater the spreading tendency will be. In practice, however, it has been found that no visible film seal occurs on cyclohexane until the SC is greater than about +3.5 to about +4.0, especially if the fluorochemical content is low. It is further known from the art that γa is reduced as the temperature of the hydrocarbon is increased, as occurs during the burning of these fuels. This will lower the effective SC during fire extinguishing unless the fire extinguishing solution also has decreasing γb on increasing temperature.
Fluorochemical surfactants have recently come under scrutiny by the EPA and environmental groups. In fact, at least one major manufacturer recently agreed to stop the manufacture of Perfluorooctanesulfonate (PFOS) and Perfluorooctanoic acid (PFOA) based products including fluorinated surfactants used in AFFF and AR-AFFF agents. The EPA, prior to May 2000, had determined that PFOS posed a long-term threat to the environment after PFOS was found in all animals tested and was determined to be toxic after various long-term feeding studies. The EPA has since initiated a program requiring other perfluorochemical producers to supply information on their products to the EPA. This would allow the EPA to evaluate potential environmental problems from other fluorochemical surfactants already in the marketplace.
It may therefore be desirable to have fire extinguishing products which do not contain fluorine-containing compounds, while still extinguishing Class B fires as effectively as AFFF agents.
The instant invention provides compositions that require little or no use of fluorochemical surfactants or other fluorine containing compounds, yet the novel fire fighting liquid concentrates still meet or exceed Fluoroprotein (FP) and Aqueous Film Forming Foam agent (AFFF) performance criteria on Class B, UL162 fires. If fluorochemical surfactant use is severely curtailed by the EPA, these agents could be important for the future of firefighting in the United States.
The commercial AFFF agent market in the United States consists most importantly of products which are UL listed such that consumers can be assured of minimum performance characteristics of AFFF agents. The UL 162 Standard for Safety covers Foam Equipment and Liquid Concentrates. Section 3.16, UL162 (Seventh edition, 1997) defines six liquid concentrates recognized by UL as low expansion liquid concentrates. Part a) defines Aqueous Film Forming (AFFF) as “a liquid concentrate that has a fluorinated surfactant base plus stabilizing additives.” Part b) defines Protein as “a liquid concentrate that has a hydrolyzed protein plus stabilizing additives.” Part c) defines Fluoroprotein (FP) as “a liquid concentrate that is similar to protein, but with one or more fluorinated surfactant additives.” Part d) defines Film Forming Fluoroprotein (FFFP) as “a liquid concentrate that has both a hydrolyzed protein and fluorinated surfactant base plus stabilizing additives.” Part e) defines Synthetic as “a liquid concentrate that has a base other than fluorinated surfactant or hydrolyzed protein. Finally Part f) defines Alcohol Resistant as “a liquid concentrate intended to extinguish both hydrocarbon and polar (water miscible) fuel fires.”
Fire test foam application and duration to burnback ignition is given in UL162 Table 10.1 for Class B fire tests. These minimum performance criteria must be met for liquid concentrates to be “UL listed” as Class B liquid concentrates. Of the six liquid concentrates defined by UL 162, only protein and synthetic do not contain fluorosurfactant and, of these, only protein has UL listed 3% products for use on Class B liquid fires. At this time, synthetic liquid concentrates are mainly UL listed as wetting agents and defined by UL as “liquid concentrates which, when added to plain water in proper quantities, materially reduce the surface tension of plain water and increases its penetration and spreading ability . . . . Listed wetting agents solutions or foams improve the efficiency of water in extinguishing fires.”
Only one synthetic, SYNDURA, commercialized by Angus Fire Armour is UL listed on Class B fires at 6% dilution rate and at the fluoroprotein application rate. Syndura utilizes a polysaccharide stabilizing agent, and although marketed as “operationally fluorine-free,” it does contain at least some fluorine.